Architectural paint and stain manufacturers typically distribute premixed paints and stains in a small number of popular colors. To accommodate consumer desires and enable matching of existing painted or stained surfaces, manufacturers typically also distribute a set of tintable paints and several concentrated colorants. These are combined at point-of-sale outlets using colorant dispensing and shaker mixing equipment to make small batch lots of custom-tinted paint in a much larger array of colors than the limited color array available in premixed products.
The custom color systems from different paint manufacturers tend to have somewhat similar components. For example, a typical custom color paint system may employ several (e.g., 2 to 4) tintable paints ranging for example from a white base intended to accept at most a small quantity of colorant, to a relatively unpigmented clear base intended to accept a much larger quantity of colorant. Base paints may employ various binders (e.g., natural or synthetic resins), binder forms (e.g., solution polymers or latex polymers) and vehicles (e.g., solvent-borne or water-borne versions), and may provide various dried surface finishes (e.g., matt, semi-gloss or gloss finishes). Some manufacturers also sell colored base paints (e.g. a red, a blue and yellow colored base) which are intended to be combined with additional colorant(s) when one coat hiding power is desired for strongly-tinted custom paint shades. The colorants in custom color paint or stain systems may, for example, be volumetrically metered from a multiple-colorant dispensing station, with 12 colorants for paint or stain typically being employed in colorant dispensing stations for the U.S. market, and more (e.g., 16 or 24 colorants) sometimes being employed in other markets.
WO2010091418 describes liquid colorants that can be used in tinting systems. Disadvantage of liquid tinting systems is the difficulty to keep the working places clean and prevent infection of mould, the phase separation of the pigments in the liquid tinting systems, which will result in inaccurate dosing of pigments and fouling of the dosing system, and the problem of evaporation of solvents, which will change the concentration of the liquid colorant and the viscosity of the liquid colorant, making the dosing inaccurate.
WO0047681, EP1474485, U.S. Pat. No. 7,318,864 and WO09074576 disclose solid pigment preparations that can be used to color paints. These solid pigment preparations are prepared in a spray drying process.
US2001/0055639 describes a process to prepare a granular product. A suspension of particles is sprayed by means of a two-fluid nozzle into liquid nitrogen. The granular product has a broad or even bimodal particle size distribution.
US2011/0262654 describes a process for making porous particles, by electrospraying a suspension of particles, collecting droplets in liquid nitrogen and then drying in vacuum. Irregular particles have been obtained.
EP0191125 describes a method to prepare solid particles by shock cooling of particles and subsequent drying of the particles by sublimation.
DE19914329 describes a method to prepare solid particles by spray drying.
EP1103173 describes a method to prepare solid pigment particles by spray drying.
All above methods prepare particles which have either an irregular shape, and/or a broad particle size distribution.
The particles prepared in a spray drying process have a number of disadvantages. They show a broad particle size distribution, contain a considerable amount of dust and turn out to be mechanically instable. The broad particle size distribution makes it necessary to include a sieving step in the process to produce the particles, which makes the process expensive and results in a low yield of suitable product. Even after sieving, the particle size distribution is still broad which causes several problems. The smaller particles (typically having a particle size below 100 μm) tend to agglomerate to aggregates that are mechanically instable and show a variable bulk density. After agglomeration the bulk density may be locally increased. At the same time small particles and large particles may show percolation, which means that the particles separate from each other: small particles drift to the lower part of a container, while larger particles tend to float on top of the smaller particles. This separation causes differences in bulk density and gives an irregular flow behavior of the particles. Moreover the particles obtained in a spray drying process do not have a regular circular shape: many particles have the shape of a ‘donut’. The ‘donut’ shape causes an increased cohesion between the particles, which has a negative influence on the flowability of the particles and influences the bulk density.
The solid pigment preparations of the prior art need to be dosed to base paint compositions in a gravimetric manner, due to the broad particle size distribution and other properties. Gravimetric dosing is usually carried out by weighing a container comprising the base paint compositions and determining the addition of the pigment preparation to the total weight of the base paint. This is complex, especially when only small amounts of solid pigment preparations should be dosed. In such cases, small variations in the environment (like vibrations and air turbulence) can cause large measuring errors, which will generate colored paint compositions that are out of specification in color. Also gravimetric measurement of the pigments means that all pigments should be dosed in a sequential manner, since each pigment should be dosed individually.
There is a need for solid colorants that can be used in tinting systems and can overcome one or more of the problems associated with the present tinting systems.
After extensive studies, the inventors solved the above mentioned problems and developed new solid colorants that can be favorably used in tinting systems for tinting base paint compositions.